Combustion and Flame Class 8 Notes: CBSE Science Chapter 4

1. Combustion:

The process in which a substance undergoes a chemical reaction in the presence of air (oxygen) to produce heat and light is called combustion.

The substance which undergoes combustion is called combustible. Combustion cannot take place in absence of oxygen. 

Ignition Temperature:

The lowest temperature at which a combustible substance catches fire under given pressure conditions is called ignition temperature. 

The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.

Controlling Fire:

Fire can be controlled by removing one or more requirements essential for producing fire. 

Water is commonly used to control fires caused by substances other than oils and electrical equipment as it can worsen the conditions. 

As water cannot be used to control fires involving electrical equipment or oils, a fire extinguisher or sand is used to put out the fire.

Types of Combustion

The type of combustion depends upon the type of fuel used. Combustions are classified on the basis of nature and intensity, which are of three types. They are: 

1. Rapid Combustion:

When a substance burns rapidly and produces heat and light, such combustion is called rapid combustion. For example, the burning of a matchstick, gas stove.

2. Spontaneous Combustion: 

The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion. For example, burning of phosphorus, burning of camphor.

3. Explosion:

A large amount of gas formed in the reaction is liberated. Such a reaction is called an explosion. For example, a firecracker, missiles.

2. Flame:

It is a zone or burning vapour caused by substances during combustion. For example Kerosene oil and LPG gas, coal etc. 

Zones of a Flame:

There are Three Different Zones of a Flame – 

• Dark Zone: Near the surface of a combustible substance which is the least hot due to incomplete combustion.

• Luminous Zone: Brightest zone due to partial combustion.

• Non-luminous Zone: The outermost part of the flame which is the hottest zone due to complete combustion. 

3. Fuel:

Fuel is any substance that undergoes combustion to obtain energy that can be used to heat or move another object.

Property of a Good Fuel:

A good fuel must: 

• Be readily available.

• Be cheap.

• Burn easily at a moderate rate. 

• Should have high calorific value.

• Do not leave behind any undesirable substances after combustion.

Fuel efficiency is expressed in terms of its calorific value which is the amount of heat energy produced on complete combustion of 1 kg of fuel and is expressed in units of kilojoule per kg(kJ/kg).

Types of Fuels: 

1. Solid Fuels: solid fuels are combustible substances that are solid at room temperature. For example: coal, camphor, wood, charcoal etc. 

2. Liquid Fuels: Volatile liquids which produce combustible vapour are called liquid fuels. These are widely used fuels in our vehicles. For example Petrol, kerosene, diesel etc. 

3. Gaseous Fuels: Combustible gases or a mixture of combustible gases are called gaseous fuels. For example: CNG, LPG, propane, biogas etc. 

Harmful Effects of Burning of Fuels: 

1. Fuels containing carbon like wood, coal or any fossil fuel release unburnt carbon particles (called suits). These are dangerous pollutants that cause respiratory diseases, such as asthma or even cancer. 

2. Incomplete combustion of carbon fuels gives carbon monoxide which is a poisonous gas and prolonged exposure can be fatal.

3. Increased concentration of carbon dioxide in the air which is called greenhouse gas is causing global warming.

4. Oxides of Sulphur and nitrogen dissolve in rainwater and form acids. Such rain is called acid rain. It is very harmful to crops, buildings and soil as it increases the acidity of the soil and corrodes the metal surface faster.

We provide the users with Ch 4 Science Class 8 notes available for free PDF download. The offline advantage makes it easier for students to study from anywhere, anytime they want without stressing about a poor internet connection. Furthermore, they also have access to a hard copy of these notes. This makes studying seamless for students as they do not have to dodge platforms to get the notes for every topic. 

Global Warming: Global warming refers to the gradual increase in Earth’s average temperature due to human activities, especially the burning of fossil fuels.

Acid Rain: Acid rain is rain that has a lower pH than normal, making it more acidic. This occurs when pollutants in the air mix with rainwater.

Causes of Acid Rain: The main cause of acid rain is the burning of fossil fuels like coal, oil, and gas. This combustion releases sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) into the atmosphere.

Formation of Acid Rain: Sulphur dioxide and nitrogen oxides react with water vapour in the atmosphere to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃). These acids then fall to the ground with the rain.

Effects on the Environment: Acid rain can harm plants, soil, and water bodies. It can damage leaves, reduce soil fertility, and lead to the acidification of rivers and lakes, affecting aquatic life.

Calorific Value of Fuel

The Calorific value is the amount of heat energy production when complete combustion of 1kg of fuel occurs. The expression for calorific value is kilojoule/kg (kJ/kg).

Here are a Few Questions For Practice to Test your Knowledge on Class 8 Science Chapter 4 Combustion and Flame

Very Short Answer Type Questions

1. What is combustion?

2. What is known as ignition temperature?

3. What is an explosion?

4. What is rapid combustion?

5. Define caloric value.

Short Answer Type Questions

1. Explain the process of acid rain.

2. What is global warming?

3. Explain the two different types of combustion.

4. What are inflammable substances?

5. How carbon dioxide helps to control fires.

Long Answer Type Questions

1. Explain the structure of a flame.

2. How can we best control fire?

3. What harmful effects are caused to the environment due to an increase in fuel consumption?

5 Important Topics of Science Class 8 Chapter 4 Combustion and flame

Importance of Class 8 Science Chapter 4 Combustion and Flame

• Revision notes help us quickly understand and remember key concepts before exams.

• They save time by focusing on essential information and skipping unnecessary details.

• These notes simplify complex topics, making them easier to understand and use.

• They provide practical examples that show how theoretical knowledge is used in real-life situations.

• Revision notes ensure thorough preparation by covering all important topics in a structured manner.

• They increase confidence by clearly understanding what to expect in exams.

• Accessible formats like PDFs allow for easy studying anytime and anywhere.

Tips for Learning the Science Class 8 Combustion and Flame Notes

• Familiarise yourself with important terms like combustion, fuel, and ignition temperature to build a solid foundation.

• Learn the three essential conditions for combustion—fuel, heat, and oxygen. Remember how each condition contributes to the burning process.

• Differentiate between various types of flames, such as luminous and non-luminous, by their characteristics and uses.

• Learn and recall basic fire safety measures and how to prevent and control fires, which is crucial for practical knowledge and safety.

• Connect the topics with real-life examples of different fuels and how they burn. This helps in understanding the practical application of theoretical concepts.

Conclusion

The revision notes for Class 8 Science Chapter 4, "Combustion and Flame," provides a clear understanding of how combustion occurs, the conditions required for it, and the different types of flames. By studying these notes, you'll learn about the key elements of burning processes, the role of different fuels, and essential fire safety tips. These notes are designed to simplify complex concepts and help you prepare effectively for exams. Remember to review the conditions for combustion, types of flames, and practical applications to reinforce your knowledge and excel in your studies.

Related Study Materials for Class 8 Science Chapter 4 Combustion and Flame

Chapter-wise Revision Notes Links for Class 8 Science

Important Study Materials for Class 8 - Science